1. Field of the Invention
The present invention relates to a device to drive various accessories such as an alternator, a cooling water pump or the like, utilizing power of an engine of an automobile or the like.
2. Description of the Prior Art
In an engine of an automobile or the like, accessories such as an alternator, a cooling water pump, an air-conditioning compressor, an oil pump for hydraulic servo steering or the like are belt-driven by a crank pulley installed at the top end of a crank shaft. Since the accessory drive is accompanied with large power loss during the high speed running of the engine, in order to avoid it, various methods have been proposed that gear shifting of a crank pulley is performed with respect to the engine rotational speed and the running speed of the accessory is limited.
In FIG. 2 illustrating an accessory drive device having such speed limiting function in the prior art, numeral 1 designates an input shaft directly coupled to a crank shaft of an engine (not shown), numeral 2 an input transmission member on the input shaft, and numeral 3 a cam device for generating pressure interposed between the input shaft 1 and the input transmission member 2. Numeral 4 designates a plurality of planetary cones, each composed of a frictional transmission surface 4a on a conical surface, a frictional transmission surface 4b on a bottom surface of cone, and a frictional transmission surface 4c on a circumferential surface of cone axial line. Numeral 5 designates a gear shifting ring which is engaged in frictional engagement with the frictional transmission surface 4a of the planetary cone 4 and moved in the axial direction so as to vary the frictional transmission radius of the planetary cone 4, and numeral 6 designates an orbit ring which is engaged in frictional engagement with the frictional transmission surface 4c of the planetary cone 4 and, in its non-rotation state, guides the revolution of the planetary cone 4 around the axial line of the input shaft 1. Numeral 7 designates an accessory drive pulley, numeral 7a a plurality of key grooves on inner circumferential surface of the pulley 7 in the axial direction, and numeral 8 a roller key which transmits the rotational force of the gear shifting ring 5 to the pulley 7 and suppresses the movement in the axial direction and is engaged with the grooves 7a. Numerals 9, 10 designate end plates to support the pulley 7 at both ends. Numeral 11 designates a stationary plate which fixedly supports the orbit ring 6 and is fixed by a mounting part 11a to the stationary member of the engine (not shown). Numeral 12 designates a frictional transmission oil which acts as medium for the frictional transmission and fills the space closed by the pulley 7, the end plates 9, 10 and the input shaft 1. Numeral 13 designates a centrifugal governor comprising a centrifugal weight, a spring plate 13a which supports the centrifugal weight and connects it to the gear shifting ring 5, and a weight 13b attached to the free end. Numeral 14 designates a return spring.
Operation of the accessory drive device will be described. The rotational force of the crank shaft of the engine is transmitted to the input shaft 1, thereby the input transmission member 2 rotates through the cam device 3. The planetary cone 4 performs self-rotation on its own axial center, and at the same time performs the revolution around the axial center of the input shaft 1 along the frictional transmission surface of the orbit ring 6 which is a stationary element. The gear shifting ring 5 engaged in frictional engagement with the frictional transmission surface 4a of the planetary cone 4 is rotated around the axial center of the input shaft 1 on the basis of the differential action between the self-rotation and the revolution of the planetary cone 4 and the transmission radius ratio, and drives the pulley 7 through the roller key 8. The rotational speed ratio between the input shaft 1 and the gear shifting ring 5 can be arbitrarily set by moving the gear shifting ring 5 in the axial direction so that the effective radius ratio of the frictional transmission between the input shaft 1 and the gear shifting ring 5 is varied. For example, if the gear shifting ring 5 is engaged in frictional engagement at the large diameter side of the planetary cam 4, the rotational speed ratio becomes 1:1, and at the small diameter side, i.e., near vertex of the cone, the rotational speed ratio becomes 1:0.4--thus reduction at side of the transmission ring 5 can be selected in nonstage state. The centrifugal governor 13 controls the axial position of the gear shifting ring 5, and automatically controls the rotational speed of the pulley 7 to the speed ratio 1:1 at low speed state of the engine and to the nearly constant rotational speed when the engine is at intermediate or high speed state. The frictional transmission oil 12 is interposed in the frictional transmission surface and acts as medium for the frictional transmission force and performs lubrication and cooling in the contacting surfaces and the bearing.
The accessory drive device utilizing the nonstage transmission with the planetary mechanism of frictional transmission type as above described has a small size and large transmission capacity. However, the frictional transmission coefficient varies depending on temperature of the frictional transmission oil as the medium of the frictional transmission, and limitation of the transmission capacity and the transmission efficiency are significantly affected. In general, the relation between temperature of the frictional transmission oil and the frictional transmission coefficient and between limitation of the transmission capacity of such transmission and the transmission efficiency is apt to decrease if the temperature of the frictional transmission oil rises. While the engine in the automobile becomes of small size and light weight, since the engine space is narrowed in order to obtain the high input and enlarge the dwelling space of the car, temperature within the engine rises and hence temperature of the frictional transmission oil of the accessory drive device rises. Therefore, the device must be of large size to compensate the decrease of the transmission capacity and the transmission efficiency is decreased.
In order to eliminate above-mentioned disadvantages in the prior art, an object of the invention is to provide an accessory drive device which decreases the temperature rise of the frictional transmission oil and has small size and good transmission efficiency.